Optical-enhanced apparatus and method for illuminating printed circuit boards for inspection

ABSTRACT

The apparatus includes: an illumination system having a planar printed circuit board, and a plurality of light producing elements mounted on the planar printed circuit board and divided into at least one area, a control system, wherein the light producing elements can be selected from at least one area and lighted to illuminate by the control system, and a flat thin lens system in front of and connected to the illumination system to focus the lights emitted from the light producing elements onto any position of the printed circuit board. The method applied to proposed apparatus includes steps of: (a) choosing a position, (b) setting the illumination conditions, (c) producing the required illumination through focusing the lights on the chosen position, (d) recording the image of chosen position, (e) displaying the image, (f) comparing the recording image with the referencing image, and (g) making a record of comparison.

FIELD OF THE INVENTION

[0001] The present invention relates to the apparatus and method forilluminating printed circuit boards for inspection. More specifically,this invention includes the apparatus and method of an optical-enhancedlighting system for using with the series of cameras associated with theprinted circuit board inspecting device.

BACKGROUND OF THE INVENTION

[0002] The optical inspection systems have been applied in many areas inindustries to reduce the manpower of quality control, prolong theworking hour, and prevent human errors, such as, searching for the dustparticles in a semi-conductor process, accurate positioning, andinspecting for missing and wrong components or soldering defects such asopen circuits, short circuit in the composition process of a circuitboard. To fulfill the above mentioned purposes, the Automated OpticalInspection Systems (AOI Systems) with a imaging system having multipleCCD (charge couple device) cameras for taking well-illuminated videoimages from multiple angles, and a micro-processor system for storingtaken video images and comparing the results from the newly taken videoimages to the standard no-fault images has been employed in thehigh-speed production lines of the electronic industry. Nowadays, theAOI Systems must have the functions for the three-dimensionalinspections to cope with the requirements of inspection regarding thealtitude of the component and the trend of more and more miniaturizationof fine-pitch ICs and SMDs (surface mount device).

[0003] The suppliers of various AOI systems are trying to offer theircustomers with new products having more advanced functions and higherspeed for inspection as well as the new applications in new areas.

[0004] To make an entry level Automatic Optical Inspection (AOI) Systemis not a difficult thing to do. To be among the best is the challenge.Most of the machine vision key components including: double speed/quadspeed CCD cameras, camera lenses, XY table, and imaging grabber cardsare available in high industrial quality. The only exception is theillumination system, the soul of AOI system, AOI makers have varioussolutions developed by their own.

[0005] Most AOI system makers use high bright light emitting diodes(LED) for illumination, such as SONY/VARIA, Teradyne, OMROM, MVP,HP/MVT, Samsung, and LG. Only Orbotech uses xenon flashes and SAKI usesfluorescent illuminators.

[0006] Currently, most types of LED illumination devices can be found incompanies like CCS Inc. Limited by the area CCD camera sensor size, toachieve a 20 um optical resolution, the inspection area per field ofview (FOV) can be only the sizes from 12 mm×9 mm to 24 mm×18 mm. Thebrighter the illumination is, the larger the depth of field or thehigher shutter speed can be. How to focus all available lights onto aspot determines the destiny of the system performance. Each type ofcommercial product available on the market offers only a single dedicatetype of illumination, for example: direct, diffused, low angle, ambient,etc. Using various combinations of different types of illumination inAOI systems are possible with penalty of larger size and higher controlcomplexity of the illumination system. Nowadays, the venders of AOIsystems develop their own illumination systems with integrated lightingcontrol capability down to section or even single individual LED levelto fulfill the illumination control multiplicity. To achieve an ambientand uniformity illumination, diffusers are often used, especially at aclose distance (See FIG. 1). However, the light output is relativelyreduced. To align each LED toward the target, a dome shape structurewith complicated fixtures is also applied with drawbacks of low LEDplacement density and short clearance/working distance (See FIG. 2). Toget the maximal LED placement density within a limited space, amulti-faceted or C-shape flexible substrate is used to form stereo spacering lighting but not focused to a spot (See FIG. 3).

[0007] Therefore, how to create an illumination system with strong,bright, uniform light and focused on a spot in a very simple physicalstructure is the goal. The Patents related to the prior arts include:U.S. patent Ser. No. 5,060,065, and U.S. patent Ser. No. 5,245,421.

[0008] Keep the drawbacks of the prior arts in mind, and employexperiments and research full-heartily and persistently, theoptical-enhanced apparatus and method for illuminating printed circuitboards for inspection are finally conceived by the applicant.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to propose anoptical-enhanced apparatus for illuminating a printed circuit board forinspection.

[0010] It is therefore another object of the present invention topropose a method for illuminating a printed circuit board forinspection.

[0011] According to the aspect of the present invention, the apparatusfor inspecting the printed circuit board includes: an illuminationsystem having a planar printed circuit board and a plurality of lightproducing elements in which the plurality of light producing elementsarranged in planar high-density arrays mounted on and electricallyconnected to the planar printed circuit board and the illuminationsystem divided into at least one area according to distances away from acentral referencing point of the illumination system, a control systemelectrically connected to the illumination system wherein the pluralityof light producing elements of the illumination system are selected fromat least one area and lighted by the control system, and a flat thinlens system having at least one flat thin lens wherein at least one flatthin lens placed in front of and tightly connected to the illuminationsystem to focus the lights emitted from the plurality of light producingelements onto any position of the printed circuit board.

[0012] Preferably, the light producing elements are light emittingdiodes.

[0013] Preferably, the flat thin lens is a Fresnel Lens.

[0014] Preferably, the apparatus further includes a camera system havingat least one camera to receive reflected lights of the printed circuitboard originally emitted from the plurality of light producing elements.

[0015] Preferably, the at least one camera is mounted right behind oneselected from a group consisting of the central referencing point of theillumination system and a plurality of locations that are equallydistanced from the central referencing point respectively.

[0016] Preferably, the at least one area can be divided into a centralarea and at least one peripheral area according to distances away fromthe central referencing point of the illumination system.

[0017] Preferably, each of the at least one peripheral area can befurther divided into at least one sub-area according to the distancesand directions away from the central referencing point of theillumination system.

[0018] Preferably, the control system controls each of the plurality oflight producing elements of the at least one area in one of on and offstatus and each of the camera of the camera system in one of on and offstatus to produce a permutation of illumination conditions including aprojecting direction, a projecting angle, and an luminous intensityshedding light on any position of the printed circuit board by theillumination system and to choose at least one camera to record an imageof a certain range centered by any position and illuminated by theillumination system when at least one light producing element of atleast one area is lighted.

[0019] Preferably, the certain range includes a size decided by a sizeof sensor of the camera and a requirement of inspecting resolution.

[0020] Preferably, the apparatus further includes a display systemhaving at least one display to show the image on a display screen.

[0021] Preferably, the apparatus further includes at least onemicroprocessor system to compare the image with a referencing imagerecord of the certain range to decide whether or not a differenceexisting and to memorize in the microprocessor system.

[0022] Preferably, the printed circuit board could be at any stage of aprocess for mounting electronic elements on the printed circuit board.

[0023] According to another aspect of the present invention, a methodusing an apparatus having an illumination system with a plurality oflight emitting diodes arranged in high-density arrays on a plane dividedinto at least one area, a flat thin lens system with at least one flatthin lens, a camera system with at least one camera, a control system, amicroprocessor system with at least one microprocessor, and a displaysystem with at least one display to inspect a printed circuit boardincludes steps of: (a) choosing a position on the printed circuit board,(b) setting a combination of illumination conditions including aprojecting direction, a projecting angle, and an illumination strengthaccording to a configuration of the printed circuit board in a certainrange using the position as a referencing center, (c) using the controlsystem to let at least one of the plurality of light emitting diodes ofat least one area of the illumination system be lighted, and to focusthe emitted lights onto the position through the flat thin lens of theillumination system to produce the combination of illuminationconditions on the position, (d) employing the control system to start atleast one camera to record a video image of the position illuminated bythe illumination system according to the combination of illuminationconditions of the position when at least one of the plurality of lightemitting diodes of at least one area of the illumination system is in“on” status, (e) displaying the video image of the position taking by atleast one started camera on a display screen of the display systemaccording to the combination of illumination conditions of the position,(f) comparing a referencing image record of the position stored in themicroprocessor system with the video image of the position to decidewhether or not a difference existing, and (g) recording whether or not adifference existing between the video image of the position and thereferencing image record of the position in the microprocessor system.

[0024] Preferably, the at least one camera of the camera system ismounted right behind one selected from a group consisting of the centralreferencing point of the illumination system and a plurality oflocations equally distanced from the central referencing pointrespectively.

[0025] Preferably, the at least one area can be divided into a centralarea and at least one peripheral area according to distances away fromthe central referencing point of the illumination system.

[0026] Preferably, each of the at least one peripheral area can befurther divided into at least one sub-area according to distances anddirections away from the central referencing point of the illuminationsystem.

[0027] Preferably, the certain range having a size decided by a size ofsensor of the camera and a requirement of inspecting resolution.

[0028] Preferably, the flat thin lens is a Fresnel Lens and is placed infront of and tightly connected to the light emitting diodes to focus thelights emitted from the plurality of light emitting diodes onto anyposition of the printed circuit board.

[0029] Preferably, the printed circuit board could be at any stage of aprocess for mounting electronic elements on the printed circuit board.

[0030] The present invention may best be understood through thefollowing descriptions with reference to the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is the schematic diagram of an illumination system of AOIsystem with flat LED arrays;

[0032]FIG. 2 is the schematic diagram of an illumination system of AOIsystem with a dome shape structure which aligns each LED on it towardthe target;

[0033]FIG. 3 is the schematic diagram of an illumination system of AOIsystem with a multi-layered LED arrays arranged in an umbrellaconfiguration;

[0034]FIG. 4 is the schematic diagram of the optical fundamentals ofFresnel Lens;

[0035]FIG. 5 is the schematic diagram showing the side view of theillumination system of the present invention; and

[0036]FIG. 6 is the schematic diagram showing the bottom view of theillumination system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] To create a strong light and focused on a spot at a very simplemanufacture process, the simple lens deflection formula is applied.Please refer to FIG. 4, an optical lenses system of infinite to finiteconjugate design can gather all parallel light rays in to a spot at thelenses focal point. Please refer to FIG. 5, if a lenses system 20 isplace in front of a plate 101 with LEDs 102 fully mounted, then thislens 20 will gather all of the LEDs lights onto a small region of areato be inspected 40. Because of the LEDs 102 are arranged in high-densityplanar arrays as an illumination system 10 at a relative longer workingdistance, this illumination system 10 can be used as a high uniformityambient-like coherent light source.

[0038] Please refer to FIG. 5, since light rays are optically bendedonto the target 40, the illumination system 10 is capable of acontinuously ambient-like illumination form near 0 degreeperpendicularly (coaxial lighting) to virtually 90 degree (ring/sidelighting) with infinity size of the disk or plate. In practice, to savethe space and cost of this optical lenses system, one or a group ofFresnel Lenses 20 are used right in front of LEDs 102 to gather thelights (See FIGS. 4 and 5). It is a reverse usage of the lens opticsthat normally used for various projection applications that port a bulblight (point light source) onto a screen. Point light sources are usedin most applications. In the prior art, the planar LED array is usedonly for direct and indirect (without and with diffuser respectively)surface light sources, simulation of parallel coherent light source assunlight and focused onto a spot is not existing till the presentinvention.

[0039] Please refer to FIG. 4, Fresnel Lens 202 is a transparent opticalmaterial thin plan with capability of focus light rays onto one pointlike ordinary optical lens. It is basically slicing an optical lens 201ring by ring and shrinking the lens thickness down to a flat thin lens(namely, a Fresnel Lens 202). It is to replace the large optical lensespecially in non-image/light source collection system to save space andcost. An illumination system using Fresnel Lens 202 can be employed notonly in improving the accuracy of inspection and accelerate the speed oftaking images of the AOI system, but also in other similar usages whichneed the optical illumination for comparisons whether the surface of theobject being inspected having flaws. Except for the inspection of aprinted circuit board, examples are the surface inspection for the flawsof an electronic element like a diode, the surface inspection for theflaws of IC chips and so on.

[0040] Please refer to FIG. 5, it is the schematic diagram showing theside view of the illumination system 10 of the present invention. Theapparatus for inspecting a printed circuit board includes: anillumination system 10 having a planar printed circuit board 101 and aplurality of light emitting diodes 102 wherein the plurality of lightemitting diodes 102 arranged in planar high-density arrays mounted onand electrically connected to the planar printed circuit board 101 andthe illumination system 10 divided into at least one area according todistances away from a central referencing point 30 of the illuminationsystem 10, a control system (not shown) electrically connected to theillumination system 10 wherein the plurality of light emitting diodes102 of the illumination system 10 can be selected from at least one areaand be lighted by the control system, and a flat thin lens system 20having at least one flat thin lens 20 wherein at least one flat thinlens 20 placed in front of and tightly connected to the illuminationsystem 10 to focus the lights emitted from the plurality of lightemitting diodes 102 onto any position of the printed circuit board 40.

[0041] Please refer to FIGS. 5 and 6, the apparatus further includes acamera system 50 having at least one camera to receive reflected lightsof an object being inspected like a printed circuit board 40 originallyemitted from the plurality of light emitting diodes 102. The at leastone camera 50 is mounted right behind one selected from a groupconsisting of the central referencing point 30 of the illuminationsystem 10 and a plurality of locations that are equally distanced fromthe central referencing point 30 respectively. The at least one area canbe divided into a central area and at least one peripheral areaaccording to distances away from the central referencing point 30 of theillumination system 10. Each of the at least one peripheral area can befurther divided into at least one sub-area according to the distancesand directions away from the central referencing point 30 of theillumination system 10. The control system controls each of theplurality of light emitting diodes 102 of the at least one area in oneof on and off status and each of the camera of the camera system 50 inone of on and off status to produce a combination of illuminationconditions including a projecting direction, a projecting angle, and anillumination strength illuminating onto any position of the printedcircuit board 40 by the illumination system 10 and to choose at leastone camera 50 to record an image of a certain range centered by anyposition and illuminated by the illumination system 10 when at least onelight emitting diodes 102 of the at least one area is lighted. Thecertain range includes a size decided by a size of sensor of the camera50 and a requirement of inspecting resolution.

[0042] The apparatus further includes a display system (not shown)having at least one display to show the image on a display screen. Theapparatus further includes at least one microprocessor system to comparethe image with a referencing image record of the certain range to decidewhether or not a difference existing and to memorize in themicroprocessor system. The printed circuit board 40 could be at anystage of a process for mounting electronic elements on the printedcircuit board 40.

[0043] Please refer to FIGS. 5 and 6 again, a method using an apparatushaving an illumination system 10 with a plurality of light emittingdiodes arranged in high-density arrays 102 on a plane divided into atleast one area, a flat thin lens system 20 with at least one flat thinlens, a camera system 50 with at least one camera, a control system (notshown), a microprocessor system (not shown) with at least onemicroprocessor, and a display system (not shown) with at least onedisplay to inspect a printed circuit board 40 includes steps of:choosing a position on the printed circuit board 40, setting acombination of illumination conditions including a projecting direction,a projecting angle, and an illumination strength according to aconfiguration of the printed circuit board 40 in a certain range usingthe position as a referencing center, using the control system to let atleast one of the plurality of light emitting diodes 102 of at least onearea of the illumination system 10 be lighted and to focus the emittedlights onto the position through the flat thin lens 20 of theillumination system 10 to produce the combination of illuminationconditions on the position, employing the control system to start atleast one camera 50 to record a video image of the position illuminatedby the illumination system 10 according to the combination ofillumination conditions of the position when at least one of theplurality of light emitting diodes 102 of at least one area of theillumination system 10 is in “on” status, displaying the video image ofthe position taking by at least one started camera 50 on a displayscreen of the display system according to the combination ofillumination conditions 10 of the position, comparing a referencingimage record of the position stored in the microprocessor system withthe video image of the position to decide whether or not a differenceexisting, and recording whether or not a difference existing between thevideo image of the position and the referencing image record of theposition in the microprocessor system. The at least one camera of thecamera system 50 is mounted right behind one selected from a groupconsisting of the central referencing point 30 of the illuminationsystem 10 and a plurality of locations equally distanced from thecentral referencing point 30 respectively. The at least one area can bedivided into a central area and at least one peripheral area accordingto distances away from the central referencing point of the illuminationsystem. Each of the at least one peripheral area can be further dividedinto at least one sub-area according to distances and directions awayfrom the central referencing point 30 of the illumination system 10. Thecertain range having a size decided by a size of sensor of the camera 50and a requirement of inspecting resolution. The flat thin lens 20 is aFresnel Lens and is placed in front of and tightly connected to thelight emitting diodes 102 to focus the lights emitted from the pluralityof light emitting diodes 102 onto any position of the printed circuitboard 40. The printed circuit board 40 could be at any stage of aprocess for mounting electronic elements on the printed circuit board40.

[0044] Although the present invention has been described and illustratedin an example of the most preferred embodiment, the constructionalcharacteristics of the present invention are not limited by that. Thevariations and modifications that anyone who is familiar with the skillcan think of easily which fall within the spirit and scope of thepresent invention as defined by the appended claims should be included.

What is claimed is:
 1. An apparatus for inspecting a printed circuitboard, comprising: an illumination system having a planar printedcircuit board, and a plurality of light producing elements in which saidplurality of light producing elements are arranged in planarhigh-density arrays mounted on and electrically connected to said planarprinted circuit board, and said illumination system is divided into atleast one area according to distances away from a central referencepoint of said illumination system; a control system electricallyconnected to said illumination system, wherein said plurality of lightproducing elements of said illumination system are selected from atleast one said area and lighted by said control system; and a flat thinlens system having at least one flat thin lens, wherein said at leastone flat thin lens is placed in front of and tightly connected to saidillumination system to focus the lights emitted from said plurality oflight producing elements onto any position of said printed circuitboard.
 2. The apparatus according to claim 1, wherein said plurality oflight producing elements are light emitting diodes.
 3. The apparatusaccording to claim 1, wherein said flat thin lens is a Fresnel Lens. 4.The apparatus according to claim 1, wherein said apparatus furthercomprises a camera system having at least one camera to receivereflected lights of said printed circuit board originally emitted fromsaid plurality of light producing elements.
 5. The apparatus accordingto claim 4, wherein said camera is mounted right behind one selectedfrom a group consisting of said central reference point of saidillumination system and a plurality of locations that are equallydistanced from said central reference point respectively.
 6. Theapparatus according to claim 5, wherein said at least one area can bedivided into a central area and at least one peripheral area accordingto distances away from said central reference point of said illuminationsystem.
 7. The apparatus according to claim 6, wherein each of saidperipheral area can be further divided into at least one sub-areaaccording to distances and directions away from said central referencepoint of said illumination system.
 8. The apparatus according to claim6, wherein said control system controls each of said plurality of lightproducing elements of said area in one of on and off status and each ofsaid camera of said camera system in one of on and off status to producea combination of illumination conditions comprising a projectingdirection, a projecting angle, and an illumination strength illuminatedonto any position of said printed circuit board by said illuminationsystem and to choose at least one said camera to record an image of acertain range centered by said position and illuminated by saidillumination system when at least one said light producing element of atleast one said area is lighted.
 9. The apparatus according to claim 8,wherein said certain range having a size decided by a size of sensor ofsaid camera and a requirement of inspecting resolution.
 10. Theapparatus according to claim 8, wherein said apparatus further comprisesa display system having at least one display to show said image on adisplay screen.
 11. The apparatus according to claim 8, wherein saidapparatus further comprises at least one microprocessor system tocompare said image with a reference image record of said certain rangeto decide whether or not a difference existed and to be memorized insaid microprocessor system.
 12. The apparatus according to claim 1,wherein said printed circuit board could be at any stage of a processfor mounting electronic elements on said printed circuit board.
 13. Amethod using an apparatus having an illumination system with a pluralityof light emitting diodes arranged in high-density arrays on a planedivided into at least one area, a flat thin lens system with at leastone flat thin lens, a camera system with at least one camera, a controlsystem, a microprocessor system with at least one microprocessor, and adisplay system with at least one display to inspect a printed circuitboard, comprising steps of: (a) Choosing a position on said printedcircuit board; (b) Setting a combination of illumination conditionscomprising a projecting direction, a projecting angle, and anillumination strength according to a configuration of said printedcircuit board in a certain range using said position as a referencecenter; (c) Using said control system to let at least one of saidplurality of light emitting diodes of at least one said area of saidillumination system be lighted, and to focus emitted lights onto saidposition through said flat thin lens of said illumination system toproduce said combination of illumination conditions on said position;(d) Employing said control system to start at least one said camera torecord a video image of said position illuminated by the illuminationsystem according to said combination of illumination conditions of saidposition when at least one of said plurality of light emitting diodes ofat least one said area of said illumination system is in “on” status;(e) Displaying said video image of said position taken by at least onesaid started camera on a display screen of said display system accordingto said combination of illumination conditions of said position; (f)Comparing a reference image record of said position stored in saidmicroprocessor system with said video image of said position to decidewhether or not a difference existed; and (g) Recording whether or not adifference existed between said video image of said position and saidreference image record of said position in said microprocessor system.14. The method according to claim 13, wherein said camera of said camerasystem is mounted right behind one selected from a group consisting ofsaid central reference point of said illumination system and a pluralityof locations equally distanced from said central reference pointrespectively.
 15. The method according to claim 13, wherein said areacan be divided into a central area and at least one peripheral areaaccording to distances away from said central reference point of saidillumination system.
 16. The method according to claim 13, wherein eachof said peripheral area can be further divided into at least onesub-area according to distances and directions away from said centralreference point of said illumination system.
 17. The method according toclaim 13, wherein said certain range having a size decided by a size ofsensor of said camera and a requirement of inspecting resolution. 18.The method according to claim 13, wherein said flat thin lens is aFresnel Lens and is placed in front of and tightly connected to saidlight emitting diodes to focus the lights emitted from said plurality oflight emitting diodes onto any position of said printed circuit board.19. The method according to claim 13, wherein said printed circuit boardcould be at any stage of a process for mounting electronic elements onsaid printed circuit board.